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p-BROMOTOLUENE                            167


p-Bromotoluene, CGH,<
Sanclmeycr, Ber., 1884,17,2651 ; Gattermann, Ber., 1890,28,
50 grins, /-toluidine.
100 c.c. cone, hydrochloric acid (in 60 c.c. water).
35 grins, sodium nitrite (in powder).
9°     «     crystallised copper sulphate (in 300 c.c.water).
45     „     potassium bromide (in 100 c.c. water).
150 c.c.   hyclrobromic acid (sp. gr. 1-49 = 47 per cent. HBr).
The ^-loluidinc is diazotiscd as described in the previous experi-
ment (Prep. 65) by forming- the hydrochloride, cooling and
gradually adding" the sodium nitrite. The solution of the
diazonium chloride is then poured into cuprous bromide dis-
solved in hyclrobromic acid. The cuprous bromide is prepared
by adding the potassium bromide solution to the copper sulphate
solution and passing in sulphur dioxide until no more precipitate
forms-. The white cuprous bromide (about 35 grams) is filtered,
washed, and well pressed on the funnel and introduced into a
round flask (i .1 litre). It is dissolved in 150 c.c. hyclrobromic acid
and well cooled in ice. The diazonium chloride is now added
slowly with constant shaking. A thick pasty mass separates and
nitrogen is evolved. When the evolution of gas has slackened
the flask is heated on the water-bath until effervescence ceases
and the bromotolucnc is then distilled in steam. The heavy
yellow liquid is extracted with chloroform, shaken with caustic
soda solution to remove traces of cresol, dehydrated over calcium
chloride, and distilled. The distillate is collected at 180—190°
On cooling, it solidifies to a pale yellow mass, m. p. 28°; b. p.
185°. Yield, 35 grams.
CI I.j.QH.t N,C1 + CuBr = CH3.C0H4Br + CuCl 4- N2.
Gattermarm's Method.—According to this method the
diazonium bromide is first prepared and then decomposed by
finely divided metallic copper. The 50 grams /-toluidine is
dissolved in 200 c.c. hyclrobromic acid previously diluted with
100 c.c. water and diazotised in the usual way. To this solution